This application is related to DE 198 37 039.3 filed on Aug. 14, 1998, which is incorporated by reference in its entirety for all purposes.
The present invention relates to a process for the TIG alternating-current welding of aluminum using an inert-gas mixture of helium and argon.
TIG welding is of great significance in the processing of aluminum. Aluminum materials have a high thermal conductivity and therefore require high levels of energy input. Furthermore, they are characterized by a high-melting oxide layer, which requires special process-engineering measures for its reliable destruction during the welding process. For this reason, in the TIG process aluminum is preferably welded under alternating current.
In the case of medium and, in particular, higher sheet thicknesses, it is often advantageous for the energy input to use mixtures of helium and argon instead of pure argon. However, increasing proportions of helium lead to arc destabilization, which can be compensated by technical equipment aspects only within certain limits.
In the view of persons skilled in the art, although higher proportions of helium in the inert-gas mixture lead to advantages in the intensification of the fusion penetration, this leads to disadvantages from process-engineering aspects, in particular to inadequate arc stability. Therefore, a helium content of 70 to 80% is regarded as the tolerable maximum.
DE-C-40 07 673 discloses a process for the inert-gas welding of aluminum with direct current, a negatively poled tungsten electrode and freehand torch manipulation, it being intended for the inert gas to consist of at least 85% helium and a residual proportion of argon. In this case, however, the end of the tungsten electrode must be of a rounded design. For this process, an inert-gas mixture containing 90% helium is offered and marketed by the Linde company under the designation VARIGON: cf. the article from Linde-KnowHow 2/97 "Ein vorteilhaftes "Paar"" [an advantageous "pair"].
Manual TIG welding with straight polarity is consequently possible in principle but nevertheless more difficult to carry out than the customary alternating-current welding. It therefore only represents an emergency solution, when no alternating-current equipment is available for a welding job; cf. A. Farwer, Krefeld and H. Wehner, Frankfurt in the article "Schutzgasschwei.beta.en" [inert-gas welding] from DVS Berichtsband 1985, page 3, left-hand column. In addition, this article provides an overview summarizing the advantages and disadvantages of this specialized area. Page 4, FIG. 9 reveals that inert-gas mixtures comprising 70% helium and 30% argon just about lead to an acceptable variation over time of current and voltage, while pure helium leads to uncertain and no longer acceptable conditions.